With the advance of techniques for manufacturing thin-film transistors, the liquid crystal displays (LCD) are widely applied in various electronic products, such as calculators, personal digital assistants (PDAs), watches, laptops, digital cameras, and mobile phones, etc. due to their advantages as smaller size, less weight, lower power consumption and no radiation. Furthermore, since manufacturers aggressively invest in research & development and employ large-scale fabricating equipment, the decreasing cost of production makes the TFT-LCD devices more popular.
Since the low-temperature poly Si (LTPS) thin film transistor LCDs are superior in resolution, brightness, size and anti-electromagnetic interferences, the LCD manufacturers are gradually focusing on such a technical field. Considering quality of films and requirements of mass production, an excimer laser annealing (ELA) is employed in the LTPS process. The excimer laser is used as a heat source and the laser light through the projection system produces laser beams with uniform energy distribution projected onto the a-Si structure on the substrate. After the a-Si structure on the substrate absorbs the energy of the excimer laser, the a-Si structure is transformed to be a poly Si structure. The entire annealing process is performed below 600° C. and a typical glass substrate or a plastic substrate can be used.
As mentioned in the above, in the application of the LTPS, the a-Si structure deposited on the substrate is irradiated and scanned by a laser beam to form laser crystallized silicons. The quality of the laser crystallized silicons has direct influences on the characteristics of various elements later formed. However, the current methods for inspecting the quality of the crystallized silicons on the substrate are not ideal. One is a method of scanning electron microscope (SEM) for examining the size, shape and distribution of the grains. Since the SEM method has to cut the substrate for sample analysis and needs a chemical pre-treatment, it cannot be directly employed on the production line and can only be used for sampling inspection due to the fact that it is destructive to the substrate. The other is a method of deep UV microscope for examining the arrangement of protrusions at the surface of the crystallized silicons. However, the deep UV microscope method can merely be used to inspect the crystallization of several microns on the substrate because it must magnify the sample to more than ten thousand times and it would take several days to inspect the whole substrate, and the equipment of the deep UV microscope method is complicated, delicate and at a high price.
Therefore, the improvements in the current inspection methods of the laser crystallized silicons in the LTPS process are urgently desired so as to provide a satisfactory inspection result of the laser crystallized silicons.